The present invention relates to power machinery. More particularly, the present invention relates to an operator presence sensor for power machinery.
Power machines, such as skid steer loaders, typically have a frame which supports a cab and a movable lift arm which, in turn, supports a work tool such as a bucket. The movable lift arm is pivotally coupled to the frame of the skid steer loader by power actuators which are commonly hydraulic cylinders. In addition, the tool is coupled to the lift arm by one or more additional power actuators which are also commonly hydraulic cylinders. An operator manipulating the skid steer loader raises and lowers the lift arm, and manipulates the tool, by actuating the hydraulic cylinders coupled to the lift arm and a hydraulic cylinder coupled to the tool. When the operator causes the hydraulic cylinders coupled to the lit arm to increase in length, the lift arm moves generally vertically upward. Conversely, when the operator causes the hydraulic cylinders coupled to the lift arm to decrease in length, the lift arm moves generally vertically downward. Similarly, the operator can manipulate the tool (e.g., tilt the bucket) by controlling the hydraulic cylinder coupled to the lift arm and the working tool to increase or decrease in length, as desired.
Skid steer loaders also commonly have an engine which drives the hydraulic pump to, in turn, power hydraulic traction motors which power movement of the skid steer loader. The traction motors are commonly coupled to the wheels through a drive mechanism such as a chain drive.
It is desirable that, under ceratin circumstances, the lift arm and the tool, or the drive mechanism, or both, be rendered inoperable. For example, in some prior devices, when an operator moves out of proper operating position in the cab of the skid steer loader, the hydraulic cylinders used to raise and lower the lift arm are locked out of operation. In such prior devices, an operator presence switch is coupled to the hydraulic circuit controlling the hydraulic cylinders to render the hydraulic lift cylinders inoperable when the operator presence switch indicates that the operator is out of proper operating position. One example of such a system is set out in the Minor et al. U.S. Pat. No. 4,389,154.
In addition, in some prior devices, moveable operator restraint bars are provided. When the operator restraint bars are moved to a retracted or an inoperative position, mechanical brakes or wheel locks lock the wheels of the skid steer loader. One example of such a system is set out in the Simonz U.S. Pat. No. 4,955,452.
Other power machinery, such as miniexcavators, typically have a base portion which is supported by a pair of track assemblies. The track assemblies are powered by hydraulic motors.
The base portion typically supports a house, or operator support portion. The house is rotatable relative to the base portion. Rotation is powered by a hydraulic slew motor. Miniexcavators also typically have a number of other features. For example, a boom is typically coupled to the house. A power actuator, such as a hydraulic cylinder, is coupled to the boom to pivot the boom relative to the house about an arc substantially located in a vertical plane. The boom is also typically pivotable substantially in a horizontal plane. This type of pivoting movement is accomplished through the use of a hydraulic cylinder (referred to as an offset cylinder) coupled to the house and to the boom.
An arm is coupled to the distal end of the boom, and is also typically pivotable relative to the boom through use of a hydraulic cylinder. A tool is commonly coupled to the end of the arm and is manipulated, also through the use of a hydraulic cylinder. Such a tool may typically be a bucket pivotally coupled to the arm.
In the above types of power machines, vehicle seat switches have been used in the past in order to determine the presence of an operator in the power machine. Such seat switches typically involve a spring, or some type of bias member which biases the seat of the power machine in an upward direction. A seat switch is generally located beneath the seat and is actuated when a load is applied to the seat and deactuated when the load is removed from the seat. The switch is typically coupled to an electrical circuit which provides a signal indicative of whether the load is applied to the seat. In addition, some conventional seat switch mechanisms are configured to operate with seats which pivot in a fore and aft direction, or seats which move in a substantially vertical direction under an operator load.
All of the above switches depend on mechanical movement of the seat. In other words, most of the prior switches require physical movement of the seat in the vertical direction in order for the switch to operate properly.